In 1994, Philips presented a catalyst system for preparing 1-hexene, etc. by trimerizing olefins, such as ethylene, particularly, a highly active and selective ethylene trimerization catalyst system using a trivalent chromium compound, a pyrrole compound, a non-hydrolyzed aluminum alkyl, and an aromatic hydrocarbon (unsaturated hydrocarbon) (U.S. Pat. No. 5,376,612). Subsequently, based on the catalyst system, 1-hexene has been commercially produced since 2003. Among various trivalent chromium compounds, a catalyst system using tris(2-ethyl hexanoate) chromium (III) (Cr(EH)3, EH=O2C8H15) exhibited superior catalytic activity. A catalyst system using Cr(EH)3 has been intensively researched and commercialized.
In the case of the catalyst system using Cr(EH)3, an aromatic hydrocarbon solvent may be prepared by, for example, adding a mixture of triethylaluminum and ethylaluminum dichloride to an aromatic hydrocarbon solvent (toluene, etc.), as a mixture of Cr(EH)3 and 2,5-dimethylpyrrole. In general, since trimerization of olefins is carried out in an aliphatic hydrocarbon solvent such as cyclohexane, an aromatic hydrocarbon solvent of a prepared catalyst system is removed through vacuum suction and then the aromatic hydrocarbon solvent-removed catalyst system is re-dissolved in an aliphatic hydrocarbon solvent such as cyclohexane. Alternatively, the catalyst system using the prepared aromatic hydrocarbon is used in a trimerization reaction and, after terminating the trimerization reaction, the aromatic hydrocarbon solvent used to prepare the catalyst is isolated and removed. In addition, when a catalyst is prepared using Cr(EH)3, a catalytic activation species is formed and thus a black precipitate is generated as a by-products, whereby a process of filtering the black precipitate is required (see U.S. Pat. No. 5,563,312). Such processes of removing and filtering an aromatic hydrocarbon solvent, such as toluene, may be a roadblock to commercialization. When the catalyst system is prepared in an aliphatic hydrocarbon solvent, such as cyclohexane, in which trimerization occurs, to omit the process of removing an aromatic hydrocarbon solvent, thermostability of a prepared catalyst is decreased. Accordingly, a catalyst is inactivated during trimerization reaction or catalyst selectivity is decreased, thus by-products, other than trimers, are generated in a large amount (see U.S. Pat. No. 5,563,312). Accordingly, in catalyst systems, etc. manufactured by Philips, aromatic hydrocarbons (unsaturated hydrocarbons) are included as essential components.
Therefore, there is a need for development of a raw material compound which does not cause the production of by-products upon preparation of a catalyst and thus does not require a filtration process, etc. and allows the preparation of a catalyst system in an aliphatic hydrocarbon solvent, and a catalyst system exhibiting superior catalytic activity upon ethylene trimerization.